The objectives of this proposed research are to isolate Fc receptors from cultured cell lines, and to characterize these receptors by immunologic and biochemical methods. Fc receptors are found on a wide variety of different cell types, and while it has been speculated that they function in the initiation and regulation of the immune response, this role has not been specifically defined. The murine leukemia, L1210, provides a homogeneous and abundant source of Fc receptor bearing cells. Two approaches of Fc receptor isolation will be used. One involves the redistribution (capping) and release of Fc receptors by the use of immune complexes bound to the cell. The other approach is to isolate Fc receptors by affinity chromatography from plasma membranes prepared by a two-phase system of polyethylene glycol and dextran. The isolated products will be analyzed by various biochemical methods in order to determine their composition and structure. Immunologic characterization will involve studying antigenic similarities and differences of Fc receptors from different cell types.